Imaging system

ABSTRACT

Imaging systems are provided allowing examination of different object regions spaced apart in a depth direction by visual microscopy and by optical coherence tomography. An axial field of view and a lateral resolution is varied depending on which object region is examined by the imaging system. The proposed imaging systems are in particular applicable for thorough examination of the human eye.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.13/116,358, filed on May 26, 2011, entitled “Imaging System”, which is acontinuation of International Patent Application No. PCT/EP2009/008433,filed Nov. 26, 2009, which is related to, and claims priority from, U.S.Provisional Patent Application No. 61/118,213, filed on Nov. 26, 2008,the disclosures of which are incorporated here by reference in theirentirety for all purposes.

FIELD OF THE INVENTION

The present invention relates to optical coherence tomography (OCT)systems and to imaging systems including an OCT system. The invention inparticular relates to imaging systems including an OCT system and amicroscope system.

BACKGROUND OF THE INVENTION

Optical coherence tomography (OCT) is an optical interferometric methodfor gaining structure information of an object. The object is disposedin a measurement arm of an interferometer and illuminated with ameasuring light, measuring light returned from the object issuperimposed with a reference light having traversed a reference arm ofthe interferometer such that the superimposed portions of light mayinterfere with each other. Intensities of the interfering light aredetected. Measuring light returning from different portions of theobject experiences different phase differences relative to the referencelight, resulting in different detected light intensities aftersuperposition with the reference light. It is possible to obtaininformation relating to structures of the object by analyzinginterference patterns obtained by such measurements.

OCT is particularly suitable to obtain high resolution information oftissue volumes of the human eye.

Different types of OCT apparatuses have been developed for imaging ofthe anterior portions of the eye and of the posterior portions of theeye.

Surgical microscopes are used to provide images of an eye to a surgeon.The images are obtained by optically imaging extended portions of theeye via oculars such that the surgeon may look into the oculars toperceive the images, or the extended portions of the eye are opticallyimaged onto a camera having an array of pixels, and light intensitiesdetected by the pixels are displayed on a display, such as a monitor ora head mounted display carried by the surgeon. Optical interference isnot involved in such imaging. Surgical microscopes are often embodied asstereoscopic microscopes providing different views of the object to theleft and right eyes of the surgeon such that the object is perceived ashaving a three dimensional structure.

It has been found desirable to provide OCT systems having an extendedapplicability and to provide imaging systems including a microscopysystem and an OCT system.

SUMMARY OF THE INVENTION

The present invention was made in view of the aforementioned problems.

According to some embodiments, the invention provides imaging systemscombining a microscope system and an OCT system.

According to some other embodiments, the invention provides imagingsystems for imaging the anterior portion of the eye.

According to still some other embodiments, the invention providesimaging systems for imaging the posterior portion of the eye.

According to still some other embodiments, the invention providesimaging systems for imaging both the anterior and posterior portions ofthe eye.

According to still some further embodiments, the invention providesimaging systems combining a microscopy system and an OCT system forimaging both the anterior and posterior portions of the eye.

According to an exemplary embodiment, an imaging system comprises anobjective lens system; a light source for generating a beam of OCTmeasuring light; and an illumination optics having adjustable opticalpower, wherein the imaging system provides a microscope facility forimaging an object region to an image region using the objective lenssystem, and an OCT facility, wherein the light source, the objectivelens system and the illumination optics are configured such that thebeam of OCT measuring light traverses the illumination optics and theobjective lens system for illuminating at least part of the objectregion with the OCT measuring light having an adjustable lateral width.

According to another exemplary embodiment, an imaging system provides anOCT facility including a light source for generating a beam of OCTmeasuring light and an illumination optics having variable optical powerfor adjusting a lateral width of the beam of OCT measuring lightilluminating at least part of an object region; and a detection systemcomprising a detector for detecting plural spectral portions of OCTmeasuring light returned from the object region and superimposed withreference light, wherein at least one of the following holds: a spectralwidth of the OCT measuring light illuminating the object region isadjustable; a spectral width of the detected plural spectral portions isadjustable.

The lateral width of a waist of the beam of the OCT measuring lightilluminating the object region is adjustable. Thus, a lateral extension,i.e. an extension transverse, in particular orthogonal, to a directionof the OCT measuring light impinging onto the object region can becontrolled by the imaging system. In particular, the OCT measuring lightilluminating at least part of the object region forms a spot at theobject region whose size is controllable. In particular the size of thespot of the OCT measuring light illuminating the object region may bechanged in a range from 100 nm to 100 μm. Further, the spot illuminatingat least part of the object region may be scanned across the objectregion to enable acquiring an image of the object region. The spot mayhave a substantially circular shape or an elongated shape, such as anellipsoidal shape.

Changing the lateral width of the OCT measuring light may also comprisedefocusing the OCT measuring light at the object region. Such defocusingmay be performed in dependence of a visual defect of an examined humaneye.

In particular, the OCT measuring light is light having a low coherencelength to perform white light interferometry.

Depending on the material comprised in the investigated object, a meanwavelength of the spectrum of the OCT measuring light and other physicalproperties, the intensity of the OCT measuring light penetrating theobject exponentially decreases characterized by a particular penetrationdepth. The penetration depth may amount for example to 1 mm to 3 mm forbiological objects such as tissue, if the mean wavelength of the OCTmeasuring light is in a range of for example 800 nm to 1300 nm. OCTmeasuring light penetrated into the object up to a particular depthwithin the object, interacts with material present within a volume atthat depth which comprises scattering and reflection processes. Inparticular, a reflectivity within a volume of the object depends on arefractive index and/or a gradient of the refractive index of thematerial within the particular volume inside the object. In particular,an intensity of OCT measuring light emanating at a particular depthwithin the object depends on a reflectivity at this depth within theobject.

The OCT measuring light having interacted with the object and emanatingfrom the object, thereby having traversed a particular probing opticalbeam path length, is superimposed with reference light having traverseda particular reference optical beam path length, and is detected. Anintensity of the detected superimposed light depends on a coherencelength of the OCT measuring light and a difference between the probingoptical beam path length and the reference optical beam path length.Only if this difference between the probing optical beam path length andthe reference optical beam path length is less than the coherence lengthof the OCT measuring light an interference signal can be detected.

Different variants of OCT differ in the way the object is probed atdifferent depths and also in the way the superimposed light is detected.

In Time-Domain OCT (TD-OCT) probing different depths of the object (i.e.performing an axial scan) is performed by varying the reference opticalbeam path length, for example by displacing a reflecting surface fromwhich the reference light is reflected. A disadvantage of this variantof OCT is however, that a mechanical displacement of the reflectingsurface must be performed involving uncertainties and inaccuracies ofthe amount of displacement as well as inaccuracies of maintaining aproper orientation of the reflecting surface.

Frequency-Domain OCT (FD-OCT) is another variant of OCT. Herein, thereference light is also reflected at a reflecting surface, but thisreflecting surface does not need to be displaced in order to probedifferent depths of the object. Instead, structure information about theobject in different depths, i.e. in particular reflectivities indifferent depths, are obtained by detecting intensities of thesuperimposed light in dependence of a wavelength of the superimposedlight.

Embodiments of the present invention employ in particular principles ofFrequency-Domain OCT. In particular, embodiments of the presentinvention employ principles of two subtypes of Frequency-Domain OCT,i.e. Spectral-Domain OCT (SD-OCT), incidentally also calledFourier-Domain OCT, and Swept-Source OCT (SS-OCT).

In Spectral-Domain OCT the light superimposed of reference light and OCTmeasuring light returned from the object is spectrally dispersed using aspectrometer, to spatially separate plural spectral portions of thesuperimposed light. Intensities of these spatially separated pluralspectral portions of the superimposed light are then detected by apositionally resolving detector. Thereby, the positionally resolvingdetector may comprise plural detector segments each of which receives aspectral portion of the superimposed light. The positionally resolvingdetector then supplies electrical signals corresponding to theintensities of the plural spectral portions representing a spectrum ofthe superimposed light. By Fourier transformation of the spectrum of thesuperimposed light a distribution of reflectivities of the object alongthe depth direction, i.e. an axial direction, is obtained.

The OCT measuring light illuminating at least part of the object regionmay be characterized by its spectrum, i.e. its normalized intensities independence of a wavelength. The spectrum of the OCT measuring light inturn may be characterized by a peak wavelength of the OCT measuringlight and a spectral width of the OCT measuring light. The spectralwidth of the OCT measuring light characterizes a width of a wavelengthrange within which most of the intensity of the OCT measuring light iscomprised. In particular, the spectral width may be determined to be aminimum of a difference between an upper wavelength and a lowerwavelength, wherein an intensity of the OCT measuring light havingwavelengths between the lower wavelength and the upper wavelengthamounts to 90% of a total intensity of the OCT measuring light. The peakwavelength of the OCT measuring light may be defined to be a mean of thelower wavelength and the upper wavelength, it may be defined as a meanwavelength of the spectrum of the OCT measuring light, or it may bedefined as a wavelength for which the spectrum of the OCT measuringlight has a maximum.

When principles of Spectral-Domain OCT are employed in embodimentsaccording to the present invention the light source generates a beam ofOCT measuring light having a peak wavelength between 800 nm and 1300 nmand having a spectral width between 5 nm and 100 nm, in particularbetween 15 nm and 30 nm. A coherence length of the OCT measuring lightis inversely proportional to the spectral width of the OCT measuringlight. In the case, where principles of Spectral-Domain OCT areemployed, the spectral width of the OCT measuring light does not need tobe adjustable. In this case the spectral width of the OCT measuringlight illuminating the object region is related to a limit of anachievable axial resolution. Further, in this case, the spectral widthof the detected plural spectral portions of the superimposed light maybe adjustable. The detection system may in this case comprise apositionally resolving detector having plural detector segments. Eachsegment of the detector may detect an intensity of a particular spectralportion of the superimposed light. For dispersing the superimposed lightin the plural spectral portions a dispersion system, for example adiffraction grating or the like, is provided.

Another subtype of Frequency-Domain OCT is Swept-Source OCT (SS-OCT).According to embodiments of the present invention principles of SS-OCTare employed. Hereby, the object region is illuminated with OCTmeasuring light having a narrow spectral width corresponding to arelatively long coherence length compared with the largest desired axialfield-of-views. During a measurement the peak wavelength of the OCTmeasuring light may be swept over a range of wavelengths spanningpreferably at least 10 nm and up to 200 nm and more. Therein the peakwavelength being in a range between 800 nm and 1300 nm, is varied independence of time, i.e. the peak wavelength is swept while detectingOCT measuring light returned from the object and superimposed withreference light by a detector, such as a photodiode. Detecting thesuperimposed light upon sweeping the peak wavelength of the OCTmeasuring light enables acquiring a spectrum of the superposed light.Again, as in the case of Spectral-Domain OCT, structure informationabout the object may be obtained by Fourier transformation of theacquired spectrum of the superimposed light. Thus, when principles ofSwept-Source OCT are employed in embodiments of the present invention,the detection system does not need to comprise a dispersion apparatusfor spectrally dispersing the superimposed light. However, in this casethe spectral width of the OCT measuring light illuminating the objectregion may be adjustable. This can be achieved for example by arrangingat least one spectral filter in a beam path of the OCT measuring lightilluminating the object region or by providing a light source generatingOCT measuring light having adjustable spectral width.

The reason for providing an adjustable spectral width of the OCTmeasuring light illuminating the object region in the case whereprinciples of that Swept-Source OCT are employed, and the reason forproviding an adjustable spectral width of the detected plural spectralportions of the superimposed light, in the case where principles ofSpectral Domain-OCT are employed, is to enable adjusting an axial fieldof view of the OCT facility. The axial field of view represents a rangeof depth within the object, from which structure information can beobtained using the OCT facility. Changing the axial field of view mayconcurrently involve changing an axial resolution. Changing the axialfield of view may have advantageous in certain applications, inparticular of ophthalmologic applications where different portions ofthe eye are examined. For example, particular anatomical structureswithin the eye may have different extensions in an axial direction, i.e.a depth direction, thus requiring different axial field of views forimaging these anatomical structures.

Further, it may be advantageous to change a lateral resolution ofstructure data generated by the OCT facility when examining differentobjects. This is enabled in embodiments of the present invention byproviding an adjustable lateral width of the beam of the OCT measuringlight illuminating at least part of the object region. In particular, alateral resolution may be defined as twice of the lateral width of thebeam of the OCT measuring light. Changing the lateral width of the beamof the OCT measuring light may partly be achieved by varying the opticalpower of the illumination optics.

According to an embodiment of the present invention the imaging systemcomprising an OCT facility further comprises an objective lens systemhaving adjustable optical power for imaging the object region to animage region, thereby providing a microscopy facility, wherein the lightsource, the objective lens system and the illumination optics areconfigured such that the beam of the OCT measuring light traverses theillumination optics and the objective lens system. Thus, an imagingsystem is provided integrating a microscopy facility and an OCTfacility, wherein the OCT facility allows to adjust an axial field ofview and a lateral resolution, and wherein the OCT measuring lighttraverses the objective lens system used to image the object region tothe image region for visual inspection by an observer.

According to an embodiment of the present invention a wavelength of theOCT measuring light is in a range between 700 nm and 1350 nm, inparticular between 1000 nm and 1100 nm. OCT measuring light having thesewavelengths may penetrate human tissue several millimeters. Inparticular, OCT measuring light having these wavelengths is suitable forexamination of a human eye.

According to an embodiment of the present invention the illuminationoptics comprises a first lens having a first focal length and a secondlens having a second focal lengths different from the first focallength, which are alternatively arrangeable in a beam path of the OCTmeasuring light, wherein a distance between an exit area of the lightsource and the first lens amounts to the first focal length, when thefirst lens is arranged in the beam path of the OCT measuring light, andwherein a distance between the exit area of the light source and thesecond lens amounts to the second focal length, when the second lens isarranged in the beam path of the OCT measuring light. In the case, whereprinciples of Spectral-Domain OCT are employed, the light source maycomprise a Super-Luminescence-Diode (SLD) and in the case, whereprinciples of Swept-Source OCT are employed the light source maycomprise an optical amplifier, such as a semi-conductor opticalamplifier (SOA), an optical fiber, such as a ring fiber, and at leastone spectral filter, such as a Fabry-Perot type spectral filter, that isarrangeable downstream the optical amplifier. Further, the light sourcemay comprise an optical fiber for supplying the OCT measuring light tothe illumination optics. In this case the exit area of the light sourcemay be considered as a tip of the optical fiber emitting the OCTmeasuring light for traversing the illumination optics. The OCTmeasuring light emitted from the tip of the optical fiber may bedescribed as a beam of OCT measuring light having a beam width and abeam divergence. In the case of a Gaussian beam the beam width is alsoknown as the beam waist. In this case the beam waist is related to thebeam divergence being a spreading angle of the beam. The beam width maybe related to a diameter of the tip of the optical fiber. When arrangedin the beam path of the OCT measuring light the exit area of the lightsource, in particular the tip of the optical fiber, is located in afocal plane of the first lens, i.e. offset by the first focal lengthfrom a principal plane of the first lens. Thus, after having traversedthe first lens the OCT measuring light substantially constitutes aparallel beam bundle having a first cross-sectional area. Whenalternatively the second lens is arranged in the beam path of the OCTmeasuring light, the tip of the optical fiber is arranged in a focalplane of the second lens, such that the OCT measuring light havingtraversed the second lens is substantially constituted by a parallelbeam bundle having a second cross-sectional area different from thefirst cross-sectional area. Thereby, a lateral width of the beam of theOCT measuring light illuminating the object region is adjustable.

Instead of or in addition to using lenses for adjusting the lateral withof the beam of the OCT measuring light also other optical elements, suchas reflective or/and diffractive optical elements, such as mirrors ordiffraction gratings, may be employed.

According to an embodiment of the present invention the imaging systemfurther comprises an OCT scanner having at least one reflecting surfacepivotable in at least one direction for scanning the OCT measuring lightbeam across the object region. The OCT scanner may be adapted to scanthe OCT measuring light beam laterally across the object region, i.e.transverse to a direction of the OCT measuring light beam impinging ontothe object. The OCT scanner may comprise two mirrors pivotable in twodifferent directions.

The OCT scanner may comprise a first mirror pivotable around a firstaxis, a second mirror pivotable around a second axis, and an imagingoptics to image a point at the first mirror on the first axis to a pointat the second mirror on the second axis.

When scanning the OCT measuring light beam across the object region theOCT measuring beam may be incident on the object region at differentposition as measuring light spots having a diameter equal to the widthof the beam of OCT measuring light at the object region. The entirety ofareas of the spots may cover an entire area of the object region.Alternatively, the spots may be separated leaving areas of the objectregion not illuminated by the OCT measuring light. In this case adistance between a center of one spot and a center of a closest otherspot may be greater than the width of the beam of OCT measuring light.

According to an embodiment of the present invention the imaging systemis configured to adapt a first operation mode, wherein the object regionis a first object region, and to adapt a second operation mode, whereinthe object region is a second object region arranged farther away, inparticular at least 20 mm, from the objective lens system than the firstobject region along a beam path of the OCT measuring light illuminatingthe object region. Thereby, the imaging system according to thisembodiment is suitable to examine an anterior portion of a human eye aswell as a posterior portion of the human eye.

According to an embodiment of the present invention the imaging systemfurther comprises an ophthalmic lens arrangeable in the beam path of theOCT measuring light between the object region and the objective lenssystem, wherein the ophthalmic lens is arranged in the beam path of theOCT measuring light between the object region and the objective lenssystem in the second operation mode, and the ophthalmic lens is arrangedoutside the beam path of the OCT measuring light in the first operationmode. Thereby, it is possible to examine in the first operation mode theanterior portion of the human eye, i.e. for example the cornea, theanterior chamber, the posterior chamber and surrounding tissue, and toexamine in the second operation mode the posterior portion of the eye,i.e. for example in particular the retina and parts of the optic nerve.

According to an embodiment of the present invention the lateral width ofthe beam of OCT measuring light illumination the object region is afirst lateral width in the first operation mode and the lateral width ofthe beam of OCT measuring light illuminating the object region is asecond lateral width in the second operation mode, which is smaller, inparticular at least two times, than the first lateral width. Thus, thelateral resolution in the second operation mode is smaller, inparticular at least two times, than the lateral resolution in the firstoperation mode.

According to an embodiment of the present invention in the firstoperation mode the spectral width of the OCT measuring lightilluminating the object region is a first spectral width of the OCTmeasuring light illuminating the first object region, and in the secondoperation mode the spectral width of the OCT measuring lightilluminating the object region is a second spectral width of the OCTmeasuring light illuminating the second object region, and wherein inthe first operation mode the spectral width of the detected pluralspectral portions is a first spectral width of the detected pluralspectral portions, and in the second operation mode the spectral widthof the detected plural spectral portions is a second spectral width ofthe detected plural spectral portions, wherein at least one of thefollowing holds: the first spectral width of the OCT measuring lightilluminating the first object region is smaller, in particular at leasttwo times, than the second spectral width of the OCT measuring lightilluminating the second object region; the first spectral width of thedetected plural spectral portions is smaller, in particular at least twotimes, than the second spectral width of the detected plural spectralportions. The smaller spectral width in the first operation mode enablesthe spectral information to be sampled more finely. The finerinformation in the spectrum results in a greater axial field of view inthe first operation mode than in the second operation mode. Thereby, anaxial field of view in the first operation mode can be adjusted to bedifferent from an axial field of view in the second operation mode. Inparticular for examining a human eye the axial field of view whenimaging the anterior portion of the eye may be larger than the axialfield of view when imaging the posterior portion of the eye in thesecond operation mode. This is in particular applicable for differenttypes of Frequency-Domain OCT facilities.

According to an embodiment of the present invention a spectral width ofthe light source is adjustable, wherein in the first operation mode thespectral width of the light source is adjusted to the first spectralwidth of the OCT measuring light illuminating the first object region,and in the second operation mode the spectral width of the light sourceis adjusted to the second spectral width of the OCT measuring lightilluminating the second object region. This embodiment is in particularapplicable, when principles of Swept-Source OCT are employed. Asmentioned above, the light source in this case may comprise a pumpedoptical amplifier that is optically connected to a ring fiber. Theoptical amplifier may have the capability to amplify light within aparticular working range of wavelengths. In the beam path of theamplified light at least one spectral filter may be arranged whosetransmission characteristics substantially defines a spectrum of lighttraversing the optical ring fiber and finally exiting therefrom forilluminating the object region. In particular, Fabry-Perot type spectralfilters may be employed comprising reflecting surfaces whose relativedistance may effect a peak wavelength of the amplified light exiting theoptical ring fiber. A characteristics of reflectivities of the opposingreflecting surfaces may effect a spectral width of the light exiting theoptical ring fiber. Thus, providing spectral filters having differentcharacteristics of their reflecting surfaces enables providing OCTmeasuring light illuminating the object region having different spectralwidths.

According to an embodiment of the present invention a peak wavelength ofthe OCT measuring light in the first operation mode and in the secondoperation mode is sweepable. Thus, the object region is illuminated withOCT measuring light having a substantially constant spectral width, buthaving peak wavelengths varying over time.

According to an embodiment of the present invention the imaging systemfurther comprises at least one spectral filter arrangeable in the beampath of the OCT measuring light illuminating the object region, whereinthe spectral filter is arranged in the beam path of the OCT measuringlight in one of the first operation mode and the second operation modeand wherein the spectral filter is arranged outside the beam path of theOCT measuring light in the other of the first operation mode and thesecond operation mode.

In particular, when principles of Spectral-Domain OCT are employed, anembodiment according to the present invention further provides aspectrometer having an adjustable dispersion strength for spectrallydispersing the OCT measuring light returned from the object region andsuperimposed with reference light to provide the plural spectralportions, wherein in the first operation mode the dispersion strength isgreater, in particular at least two times, than in the second operationmode. A spectrometer spatially separates different spectral portions ofthe superimposed light. The greater the spatial separation of thespectral portion the greater the dispersion strength. The spectrometermay comprise refractive and/or diffractive and/or reflective opticalelements. These may comprise for example a diffraction grating, a lens,a prism, and the like. Different dispersion strengths may be realized byproviding for example two diffraction gratings having different latticeconstants which are alternatively arrangeable for dispersing thesuperimposed light. Alternatively, an optical system having variableoptical power may be arranged downstream of a diffraction grating toalter the special separation of the plural spectral portions dispersedby the diffraction grating. This may involve displacing a positionallyresolving detector in dependence of the adjusted optical power of theoptical system.

According to an embodiment of the present invention the spectrometercomprises a lens system having variable optical power arranged upstreamof the detector.

According to an embodiment of the present invention the detector is aspatially resolving detector. The detector may comprise several detectorsegments, such as pixels, which individually detect intensities of lightimpinged thereon. A spectral width of light received by a singledetector element is related to the axial field of view of the structuredata acquired by the OCT facility.

The foregoing as well as other advantageous features of the inventionwill be more apparent from the following detailed description ofpreferred embodiments of the invention with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically illustrates an imaging system according to anembodiment of the present invention in a first operation mode;

FIG. 1B schematically illustrates the imaging system according to FIG.1A in a second operation mode;

FIG. 2 schematically illustrates an imaging system, in particular aSpectral-Domain OCT facility according to an embodiment of the presentinvention;

FIG. 3 schematically illustrates an imaging system, in particular aSwept-Source OCT facility, according to an embodiment of the presentinvention; and

FIG. 4 illustrates a diagram of a spectrum of OCT measuring light thatmay be used in the Swept-Source OCT facility according to FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A schematically illustrates an imaging system 1 according to anexemplary embodiment of the present invention in a first operation mode.Imaging system 1 provides a microscope feature embodies as a microscopeportion 3 as well as an OCT feature embodied as an OCT portion 5. In theillustrates example, a human eye 7 is investigated using the imagingsystem 1. The microscope portion 3 allows visual inspection of the eye7, in particular visual stereoscopic inspection of the eye 7. Inparticular, microscopic images of the eye 7 may be acquired. For thispurpose, the eye 7 is illuminated by a microscopy illumination lightsource (not shown in FIG. 1A) generating microscopy illumination lighthaving wavelengths in the visible wavelength range. Depending on theapplication, an angle of incidence of the microscopy illumination lightand a colour temperature of microscopy illumination light may be varied.In spite of these possible adaptations regarding the microscopyillumination light, it is not easy to inspect the eye 7 by visualinspection only, since the eye comprises a number of transparentanatomical structures that can hardly be resolved or recognized.Therefore, for a thorough investigation of the eye 7 the imaging system1 provides an OCT feature by the OCT portion 5. The OCT feature allowsto acquire structural volume data of the eye 7. Thus, the OCT facilityallows acquiring data across a lateral extension and a depth (or axial)extension of the eye 7.

The imaging system 1 according to the illustrated example allows toinspect the eye 7 by visual microscopy and optical coherence tomographyboth in the anterior portion of the eye 7 and in the posterior portionof the eye 7. For this, the imaging system 1 is configured to provide afirst operation mode for inspecting the anterior portion, as illustratedin FIG. 1A, and a second operation mode for inspecting the posterior, asillustrated in FIG. 1B.

The imaging system 1, comprises an objective lens system 9 havingadjustable optical power that is located in a beam path of both themicroscope portion 3 and the OCT portion 5. The microscope portion 3comprises a stereoscopic optical system downstream the objective lenssystem. This stereoscopic optical system comprises a zoom system 11comprising a zoom lens 11 ₁ and zoom lens 11 ₂ and an ocular system 13comprising an ocular lens 13 ₁ which is viewed by a left eye 14 ₁, andan ocular lens 13 ₂. which is viewed by a right eye 14 ₁ of an observer.In the first operation mode illustrated in FIG. 1A the objective lenssystem is adjusted to have a focal length fo₁. In a focal plane 15 ₁ ofthe objective lens system 9 adjusted to have a focal length fo₁ theobject region 17 ₁ is arranged. The object region 17 ₁ includes theanterior portion of the eye 7. The anterior portion of the eye comprisesfor example the cornea, the anterior chamber, the posterior chamber anda crystal lens 8 of the eye 7. Microscopy illumination light isscattered and reflected from the object region 17 ₁ and emergestherefrom as light 19. The light 19 traverses the objective lens system9. One part of light 19 traverses the zoom lens 11 ₁ and thereafter theocular lens system 13 ₁, to enter e.g. the left eye 14 ₁ of theobserver. Another part of the light 19 having traversed the objectivelens system 9 traverses the zoom lens 11 ₂ and the ocular system 13 ₂ toenter the right eye 14 ₂ of the observer, such that the observerperceives a stereoscopic image of the object region 17 ₁. The microscopeportion may comprise a beam splitter 121 arranged downstream of theobjective lens in the beam path of one or both parts of the light 19 todirect these parts of light 19 a image sensors 123, such as a CCDdetectors, in order to record and store electronic representations ofimages of the object region 17 ₁. These recorded images can be displayedvia displays, such as a monitor, in particular a stereo display, or ahead mounted display 125 carried by the observer.

The OCT portion 5 includes a spectrometer 21 which includes a lightsource, a beam splitter, a reference arm and a detector. The measuringarm of the interferometer carries OCT measuring light 23 that issupplied to an optical fiber 25. The optical fiber 25 guides the OCTmeasuring light 23 to a tip 27 of the optical fiber 25 which representsan exit area of the light source comprised in OCT spectrometer 21. Theexit area at the tip 27 of the optical fiber 25 may correspond to a tipend of the core of the optical fiber 25 which guides the OCT measuringlight 23. The OCT measuring light 23 emanates from the exit area at thetip 27 of the optical fiber as a divergent beam.

The exit area at the tip 27 of the optical fiber from which the OCTmeasuring light 23 emanates is arranged in a focal plane 28 of acollimating lens 29 ₁. The focal length of the collimating lens 29 ₁amounts to fc₁. The OCT measuring light 23 traverses the collimatinglens 29 ₁ and is collimated to form a substantially parallel beam bundlehaving a cross sectional diameter d₁. Thereafter, the collimated OCTmeasuring light enters a scanning system 31 including a first scanningmirror 33 pivotable about a first axis and a second scanning mirror 35pivotable about a second axis extending in a direction different from adirection of extension of the axis of the first mirror. The scanningsystem 31 is provided to enable scanning of the OCT measuring lightacross the object region 17 ₁.

After being reflected at the scanning mirrors 33 and 35 the OCTmeasuring light is reflected at a mirror 37 to direct the OCT measuringlight 23 towards the objective lens system 9. In the illustratedexample, the mirror 37 is arranged between the two stereoscopic beampaths traversed by the microscopy light 19. According to other examples,the mirror 37 is a semi-transparent mirror traversed by the microscopylight 19.

After being reflected from the mirror 37, the OCT measuring light 23traverses the objective lens system 9 to be focused at the focal plane15 ₁ of the objective lens system 9 being adjusted to have the focallength fo₁. Thus, the exit area at the tip 27 of the optical fiber 25 isimaged by the collimating lens 29 ₁ and the objective lens system 9 ontoa part of the image region 17 ₁. A size of the image of the exit area atthe tip 27 of the optical fiber 25 determines a lateral width of thebeam of the OCT measuring light 23 illuminating at least part of theobject region 17 ₁. The lateral width of the beam of the OCT measuringlight 23 illuminating part of the object region 17 ₁ limits a lateralresolution of the OCT portion.

The objective lens system 9 and the collimating lens 29 ₁ form theillumination optics of the OCT portion 5 in the first operation mode. Amagnification of this illumination optics, i.e. a ratio of a size of animage of an object and a size of the object, is given as a ratio betweenthe focal length of the objective lens system 9, i.e. fo₁, and the focallength of the collimating lens 29 ₁, i.e. fc₁. Thus, the magnificationis fo₁/fc₁. Therefore may vary

The magnification of the illumination optics can be varied by varyingthe focal length fo₁, the focal length fc₁ or both focal lengths fo₁ andfc₁. Such variation results in a variation of the lateral width of theOCT measuring light illuminating the object region 17 ₁. It follows thatthe lateral resolution of the OCT portion of the imaging system can bevaried by such variation of the one or both of the focal lengths fo₁ andfc₁.

The OCT measuring light 23 penetrates the object region 17 ₁, i.e. theanterior portion of the eye 7, in a depth direction, i.e. a directionsubstantially orthogonal to the focal plane 15 ₁. The OCT measuringlight 23 interacts with tissue material within a volume portion definedby the lateral width of the OCT measuring light. Portions of the OCTmeasuring light are reflected at different positions with differentstrength depending on optical properties of tissue material located inthis volume portion. Having interacted with the object region 17 ₁ theOCT measuring light emerges as light 39 from the eye 7. The light 39traverses the objective lens system 9, is reflected from the mirror 37,is reflected from the scanning mirrors 35 and 33, traverses thecollimating lens 29 ₁, enters the tip 27 of the optical fiber 25 and isguided to a the beam splitter of the interferometer 21. At the beamsplitter, the light 39 is superimposed with reference light havingtraversed the reference arm of the interferometer 21. The superimposedlight generates an interference on a detector of the OCT portion.

According to time-domain OCT, a length of the reference arm of theinterferometer is varied, and the detected light intensities arerecorded in dependence of the length of the reference arm. Theintensities recorded in dependence of the length of the reference armare analyzed to obtain volume data representing the tissues of theanterior portion of the eye 7.

According to spectral-domain OCT, the superimposed light is guided to aspectrometer which disperses the superimposed light based on itswavelength and detects intensities of plural spectral portions of thesuperimposed light. Thereby, a spectrum of the superimposed light isobtained. Electrical signals corresponding to the spectrum are thensupplied via signal line 41 to a control and processing system 43. Thecontrol and processing system 43 processes the electrical signals, suchas performing a Fourier transformation, sampling, normalization and thelike to compute volume data representing tissues of the eye 7 within theobject region 17 ₁.

Moreover, other embodiments can use other OCT methods, such as sweptsource OCT for obtaining the volume data representing tissues of the eye7 within the object region 17 ₁.

In order to allow communication with a user, an input unit 45, such as akeyboard and a mouse, and a display unit 47 for visualizing the volumedata, such as a monitor, can be connected to the control and processingsystem 43. Via a signal line 49 the control and processing system 43 isalso connected to the scanning unit 31, to control rotational movementsof the mirrors 35 and 33, in order to scan the beam of OCT measuringlight 23 across the object region 17 ₁.

Further, the control and processing unit 43 controls via the signal line41 the spectrometer comprised in the interferometer 21 in order toadjust a dispersion strength of the spectrometer. The dispersionstrength of the spectrometer is related to the spectral resolution ofthe detected spectrum of the dispersed superimposed light, and thus tothe spectral width of the detected plural spectral portions of thedispersed superimposed light. This spectral resolution is related to anaxial field of view (FOV) of the obtained OCT data. The spectral widthis also related to an axial field of view of the OCT data. The field ofview corresponds to a depth range within the object region from whichstructure information can be obtained by the OCT portion. In the firstoperation mode the dispersion strength of the spectrometer is adapted bythe control and processing system 43 such that the field of view isFOV₁, as indicated in FIG. 1A.

In a time-domain OCT system, the field of view is FOV₁ is adjusted bycontrolling a scanning movement of a mirror in the reference arm of theinterferometer.

Further, via signal line 51 the control and processing unit 43 controlsan actuator 53 being adapted to rotate a carrier or shaft 55 on whichthe collimating lens 29 ₁ and a further collimating lens 29 ₂ areattached. In other embodiments, the collimating lenses 29 ₁ 29 ₂ areattached to a slider moved by the actuator to be translated in a lineardirection.

The actuator 53 is controlled by the control and processing unit 43 toarrange either the collimating lens 29 ₁ or the collimating lens 29 ₂into a beam path of the OCT measuring light 23 downstream the exit areaat the fiber tip 27 of the optical fiber 25. The collimating lenses 29 ₁and 29 ₂ have different focal lengths, the collimating lens 29 ₁ hasfocal length fc₁ and the collimating lens 29 ₂ has focal length fc₂ thatis greater than the focal length fc₁. As explained above, changing thefocal length of the collimating lens changes the lateral width of theOCT measuring light 23 illuminating the object region 17 ₁ or objectregion 17 ₂ as explained below.

Thus, the control and processing unit 43 is capable of controlling thelateral width of the OCT measuring light illuminating the object region,and thus of adjusting the lateral resolution of structural data acquiredby the OCT portion 5.

According to a particular example in the first operation mode, the exitarea at the tip 27 of the optical fiber 25 may have a diameter of around5 μm, and a lateral width of the OCT measuring light 23 at the objectregion may be around 60 μm, thus requiring a magnification of theillumination optics comprising the collimating lens 29 ₁ and theobjective lens system 9 of around 10. This magnification may for examplebe achieved, if the focal length fo₁ of the objective lens system 9 isaround 200 mm and the focal length fc₁ of the collimating lens 29 ₁ isaround 20 mm. The dispersion strength of the spectrometer of the OCTfacility may be adjusted such that the field of view in the firstoperation mode, i.e. FOV₁, is around 3 to 7 mm.

Further, via signal line 57 the control and processing system 43 cancontrol by appropriate actuators a magnification of the zoom system 11.The magnification of the zoom system 11 may in particular be controlleddepending on a size of a scanning area of the OCT measuring light 23which is defined by maximum rotations of the scanning mirrors 33 and 35.In particular, the control and processing system 43 may be adapted tosubstantially match a size of a microscopic field of view determined bya magnification of the zoom system 11 and the size of the scan area ofthe OCT measuring light. For example, if a user manually changes themagnification of the zoom system 11, the control and processing system43 can automatically control the scanning unit 31 to match the scan areaof the OCT measuring light with the microscopic field of view.

FIG. 1B schematically illustrates the imaging system 1 illustrated inFIG. 1A in the second operation mode. In the second operation mode anobject region 17 ₂, i.e. the posterior portion of the eye 7, isinvestigated. For this purpose, several components of the imaging system1 have been readjusted compared to their condition during the firstoperation mode illustrated in FIG. 1A: An actuator 61, which can bemanually controlled or controlled via signal line 59 by the control andprocessing system 43, mounts an ophthalmic lens 63 between the objectivelens system 9 and the eye 7. Optionally, the focal length of theobjective lens system 9 has been manually adjusted or adjusted viasignal line 10 by the control and processing system 43 to be fo₂.Further, an inversion system 65 has been introduced into the beam pathof the light 19 to compensate up-down and right-left inversion caused byintroducing the ophthalmic lens 63 such that the image perceived by theuser looking into the oculars 13 is an upright image.

Further, the collimating lens 29 ₁ has now been replaced by collimatinglens 29 ₂ to be arranged in the beam path of the OCT measuring light 23downstream the exit area at the tip 27 of the optical fiber 25.Collimating lens 29 ₂ has a focal length fc₂ and the exit area at thetip 27 is arranged in the focal plane 28 of the collimating lens 29 ₂.The focal length fc₂ is greater than the focal length fc₁. In theillustrated example, the focal length fc₂ is two times the focal lengthfc₁. In particular, the focal length fc₂ may be about 30 mm to 50 mm.The effect of the change from the collimating lens 29 ₁ in the firstoperation mode to the collimating lens 29 ₂ in the second operation modeis that the lateral width of the OCT measuring light illuminating nowthe object region 17 ₂ is decreased, for example by a factor of morethan 2.

The OCT measuring light 23 emanating as a divergent beam from the tip ofthe optical fiber 25, traverses the collimating lens 29 ₂, is reflectedfrom the scan mirrors 33 and 35 as substantially parallel beam bundle,is reflected by the mirror 37, traverses the objective lens system 9 tobe focused at the focal plane 15 ₂ which is arranged a distance fo₂ awayfrom the objective lens system 9. At the focal plane 15 ₂ the convergentOCT measuring light 23 crosses, and traverses the ophthalmic lens 63, toform a substantially parallel beam bundle. This substantially parallelbeam bundle of OCT measuring light 23 traverses the crystal lens 8 ofthe eye to be focused on the retina 18 of the eye in the object region17 ₂. The OCT measuring light 23 interacts with the object region 17 ₂in a depth range corresponding to the axial field of view FOV₂ andleaves the object region 17 ₂ as light 39. Light 39 traverses thecrystal lens 8, the ophthalmic lens 63, the objective lens system 9, theinversion system 65, is reflected at the folding mirror 37, the twoscanning mirrors 35 and 33, traverses the collimating lens 29 ₂ and issupplied to the optical fiber 25 which guides the light 39 to theinterferometer 21 of the OCT facility 5, as described above.

In the second operation mode the dispersion strength of the spectrometer(within interferometer 21) for wavelength dispersion of the light 39superimposed with reference light has been set to be smaller than in thefirst operation mode. Thus, the axial field of view in the secondoperation mode, i.e. FOV₂, is smaller, in particular more than two timessmaller, than the field of view in the first operation mode, i.e. FOV₁.Thus, for switching from the first operation mode to the secondoperation mode the control and processing system 43 has at leastcontrolled the actuator 53 to cause switching from the collimating lens29 ₁ to the collimating lens 29 ₂. The control and processing system 43may also control the spectrometer to change the dispersion strength. Thecontrol and processing system 43 may also control the objective lenssystem 9 to change from the focal length from fo₁ to fo₂. The controland processing system 43 may also control may also control the actuator61 to place the ophthalmic lens 63 in a beam path of the OCT measuringlight and the microscopic light thereby changing from the object region17 ₁ to the object region 17 ₂ which is located farther away from theobjective lens system 9 than the object region 17 ₁.

FIG. 2 schematically illustrates another embodiment 1 a of an imagingsystem. As will be explained below, the imaging system 1 a may also beused to provide the OCT portion 5 of the embodiment illustrated withreference to FIGS. 1A and 1B above. The imaging system 1 a provides anOCT feature embodied as a Spectral Domain OCT. The OCT portion 5 acomprises a light source 67 for generating a beam of OCT measuring light23′ which is guided by an optical fiber 69 to a beam splitter/coupler71. The beam splitter/coupler 71 splits the OCT measuring light 23′ intoa portion 23 and a portion 24. Portion 24 of the OCT measuring light isguided via an optical fiber 69 to a reference mirror 73 which can bedisplaced in directions indicated by double arrow 74. Portion 24 of theOCT measuring light is reflected from the reference mirror 73 and isguided as light 24′ to the optical splitter/coupler 71. Portion 23 ofthe OCT measuring light is guided by optical fiber 25 a to a tip 27 a ofthe optical fiber 25 a from which the portion 23 of the OCT measuringlight emanates as a divergent beam and traverses a collimating optics 29a having adjustable optical power. The collimating optics 29 a may beconstructed as a zoom system such that a focal length thereof can bechanged continuously or in one or more steps. The OCT measuring light 23is collimated by collimating optics 29 a, is reflected from mirrors 33 aand 35 a of a scanning system 31 a, traverses a lens system 9 a to befocused in a focal plane 15 a of the lens system 9 a in object region17. Light 39 emanating from the object region traverses lens system 9 a,is reflected from the scanning mirrors 35 a and 33 a, traverses thecollimating optics 29 a, enters the optical fiber 25 a and is guided tothe beam splitter/coupler 71, where it is superimposed with the lightportion 24′, to form superimposed light 26. Superimposed light 26 isguided via optical fiber 69 to a spectrometer 75.

Spectrometer 75 includes a dispersion apparatus 77, imaging optics 79and a spatially resolving detector 81. The dispersion apparatus 77 maycomprise diffractive and/or refractive optical elements for dispersingthe superimposed light 26. Dispersing the superimposed light 26typically comprises deflecting spectral portions of the superimposedlight 26 in different directions depending on wavelengths comprised inthe spectral portions. The dispersion apparatus 77 may for examplecomprise a diffraction grating including a substrate having pluraldiffractive elements arranged thereon, in particular arranged in aperiodic manner. The dispersion apparatus 77 disperses the superimposedlight 26 into plural spectral portions 83. The plural spectral portions83 traverse the imaging optics 79 having adjustable optical power. Thedetector 81 is arranged in the focal plane 84 of the imaging optics 79.Thus, a distance between an effective surface 82 of the detector 81 anda principal plane of the imaging optics 79 corresponds to the focallength fi of the imaging optics 79. When the focal length fi of theimaging optics 79 is changed, the detector 81 is shifted in directionsindicated as double arrow 85 to keep the effective surface 82 of thedetector 81 arranged in the changed focal plane 84 of the imaging optics79. The detector 81 comprises plural detector segments each receiving aparticular spectral portion 83 of the dispersed superimposed light 26.By changing the focal length fi of the imaging optics 79 and displacingthe detector 81 as explained above, a width of a wavelength rangecomprised in a spectral portion received and detected by a singledetector segment can be controlled. This width of a wavelength rangedetected by a single detector segment is related to the axial field ofview provided by the OCT facility 5 a. Thereby, the OCT facility 5 a isenabled to adjust an axial field of view to for example a value of FOV₁or a value of FOV₂, as indicated in FIG. 2.

Further, by varying the focal length fc of the collimating optics 29 aand arranging the fiber tip 27 a in the focal plane 28 a of thecollimating optics 29 a the lateral width of the beam of OCT measuringlight 23 illuminating the object region 17 can be controlled. Thus, theOCT facility 5 a is also capable of adjusting a lateral resolution.

As explained above, the imaging system 1 a providing an OCT feature maybe employed as the OCT portion 5 in the imaging system 1 illustratedwith reference to FIGS. 1A and 1B above. For this purpose, the OCTmeasuring light 23 may be guided through the objective lens system 9instead of the lens system 9 a by providing a mirror 37 a instead of thelens system 9 a as indicated by double arrow 38.

The imaging system 1 a also comprises a control and processing system 43a performing similar functions as the control and processing system 43of imaging system 1 illustrated in FIGS. 1A and 1B illustrated withreference to FIGS. 1A and 1B above. In particular, the control andprocessing system 43 a obtains data from the detector 81 via signal line41 a and controls also displacing the detector 81 in directionsindicated by double arrow 85. Further, system 43 a controls adjusting ofthe focal length fi of the imaging optics 79 and thus controls adjustingthe dispersion strength of the spectrometer 75. Further, via signal line51 a the control and processing system 43 a controls adjusting the focallength fc of the collimating system 29 a.

FIG. 3 illustrates another embodiment of an imaging system 1 baccording. In particular, FIG. 3 schematically illustrates an imagingsystem 1 b providing an OCT feature embodied as a swept-source OCT. Theswept-source OCT 5 b illustrated in FIG. 3 can be used to form providethe OCT portion in the embodiment illustrated with reference to FIGS. 1Aand 1B above. In particular, also the swept-source OCT 5 b illustratedin FIG. 3 can be controlled to adjust an axial field of view of the OCTimaging as well as a lateral resolution of the OCT imaging.

The swept-source OCT 5 b comprises an optical amplifier 87 foramplifying light waves in a predetermined wavelength range. For thispurpose, the optical amplifier 87 can be a semi-conductor opticalamplifier pumped by a current source 89. The optical amplifier 87 isoptically connected to a ring fiber 91 for guiding light amplified bythe optical amplifier 87. In a beam path provided by the optical fiber91 routing switches 93 and 95 are configured to guide light propagatingwithin the optical fiber 91 to optical fiber 91 ₁, 91 ₂, and 91 ₃.Optical fiber 91 ₁ guides light received from routing switch 93 orrouting switch 95 to a first sweepable filter 97 ₁. After traversing thefirst sweepable filter 97 ₁ the filtered light is again coupled into thefiber ring 91 via routing switch 93 or 95.

Alternatively to traversing the first sweepable filter 97 ₁ the routingswitches 93 and 95 may cause the light in the ring 91 to be guidedthrough a second sweepable filter 97 ₂ or a third sweepable filter 97 ₃.The first, second and third sweepable filters 97 ₁, 97 ₂, and 97 ₃ maybe spectral filters of the Fabry-Perot type comprising two opposingreflecting surfaces arranged parallel to each other. A distance betweenthe two reflecting surfaces is can be controlled by a piezo-electricelement controlled by a ramp generator 99 connected to the threespectral filters. Only light having a wavelength satisfying a resonancecondition depending on a distance between the two opposing reflectingsurfaces of the spectral filter arranged in the beam path of the ring 91will constructively interfere. Light having other wavelengths willsubstantially be attenuated. By changing the distance between the twoopposing reflecting surfaces of the Fabry-Perot type filter using theramp generator 99, a peak wavelength of light satisfying the resonancecondition can be varied. Depending on the optical properties of theopposing reflecting surfaces of the Fabry-Perot type filter arranged inthe beam path of the ring fiber 91 not only a single wavelength willsatisfy the resonance condition but a range of wavelengths around thepeak wavelengths. Thus, a particular Fabry-Perot type spectral filter ischaracterized by a particular transmission spectrum whosecharacteristics depends on at least a reflectivity of the reflectingsurfaces.

FIG. 4 is a diagram showing transmission characteristics T of the firstand second sweepable filters 97 ₁ and 97 ₂. Depending on the wavelengthλ, a transmission of the first sweepable filter 97 ₁ is shown as a curve101 ₁, and a transmission of the second sweepable filter 97 ₂ is shownas a curve 101 ₂. Typically, each Fabry-Perot type filter exhibitsseveral transmission peaks. In FIG. 4 two such transmission peaks P, P′are shown, one having a mean wavelength of 1000 nm and another having amean wavelength of 1100 nm. Plural transmission peaks occur, because theresonance condition may be satisfied by plural wavelengths according todifferent orders. Here, only the first transmission peak P locatedaround 1000 nm is of interest, since the second transmission peak P′located around 1100 nm is located outside the working range of thesemi-conductor optical amplifier 87 and is therefore not amplified.

As first spectral width 105 ₁ of the transmission spectrum 101 ₁ of thefirst sweepable filter 97 ₁ may be obtained by forming a minimum of adifference between two wavelengths 102 ₁ and 104 ₁ within which 90% ofthe transmission 101 ₁ of the first sweepable filter 97 ₁ is comprised,whereby transmission peaks of higher order wavelengths outside thewavelength range of the semi-conductor optical amplifier 87 aredisregarded. In the illustrated example, the first spectral width 105 ₁amounts to about 50 μm. Similarly, a second spectral width 105 ₂ of thetransmission spectrum 101 ₂ of the second sweepable filter 97 ₂ may beobtained amounting to about 20 μm.

Referring again to FIG. 3, when the first sweepable filter 97 ₁ isarranged to be traversed by light guided within the ring fiber 91, onlylight will be amplified by the semi-conductor optical amplifier 87 thatsubstantially has a spectrum given by the transmission spectrum 101 ₁ ofthe first sweepable filter 97 ₁, as illustrated in FIG. 4. Thus, aspectrum of light guided within the ring fiber 91 will be largelydefined by the transmission characteristics of the spectral filter 97 ₁arranged within the ring fiber 91. Light thus amplified will be denotedas OCT measuring light 107. A portion of the OCT measuring light 107 isextracted by splitter 109 and is guided to interferometer 111. In theinterferometer 111, the OCT measuring light is split into two portions,wherein one portion is reflected by a reference mirror and the otherportion is directed to collimating optics 29 b. The collimating optics29 b has an adjustable optical power similar to the collimating optics29 illustrated in FIGS. 1A and 1B and collimating optics 29 aillustrated in FIG. 2. Thus, these different embodiments of collimationoptics provide a similar function in controlling a lateral width of OCTmeasuring light illuminating the object region 17 where the object 7 isarranged.

After having traversed the collimating optics 29 b the OCT measuringlight 107 traverses the lens system 9 b to be focused at the objectregion 17. The OCT measuring light 107 illuminating the object region 17interacts with the object 7, and light 39 emanates from the object,traverses the lens system 9 b, collimating optics 29 b and is guided tointerferometer 111. Here, light 39 is superimposed with reference lightto form superimposed light 26 b. Superimposed light 26 b is guided tophoto detector 113 which detects an intensity of the superimposed light26 b.

Similar to the other embodiments of imaging systems illustrated above,the imaging system 1 b comprises a control and processing system 43 bthat controls operation of the imaging system 1 b. In particular,control and processing system 43 b controls, via a signal line 98, theramp generator 99 to enable sweeping of the peak wavelength of the OCTmeasuring light 107. Further, the system 43 b may control adjusting thefocal length of the collimating optics 29 b and may also control therouting switches 93 and 95, thereby controlling a spectrum of the OCTmeasuring light 107 illuminating the object region 17. Thus, the controland processing system 43 b may control and change an axial field of viewand/or a lateral resolution of the OCT portion 5 b.

When the lens system 9 b is substituted with folding mirror 37 of theimaging system 1 illustrated in FIGS. 1A and 1B the OCT facility 5 b maybe used as OCT facility 5 in the imaging system 1 illustrated in FIGS.1A and 1B.

Embodiments of the present invention provide imaging systems enablingexamination of both the anterior portion of the eye and the posteriorportion of the eye by visual microscopy and optical coherencetomography. In particular, these imaging systems allow switching of OCTcomponents and microscopy components when examining the one or the otherobject region. In particular, an axial field of view and a lateralresolution of the OCT method are varied when switching the objectregions.

While the present invention has been shown and described herein in whatis believed to be the most practical and preferred embodiments, it isrecognized that departures can be made therefrom within the scope of theinvention, which is therefore not be limited to the details disclosedherein but is to be accorded the full scope of the claims so as toembrace any and all equivalent methods and apparatus.

The invention claimed is:
 1. A method of inspecting an eye, the methodcomprising: operating an imaging system in one of a first mode ofoperation and a second mode of operation; wherein the imaging systemcomprises a microscope system and an OCT system; wherein the microscopesystem is configured to image an object plane onto an image plane andwherein the OCT system is configured to generate an OCT measuring beamof OCT measuring light; wherein the object plane is located in a regionof an anterior portion of the eye in the first mode of operation, andthe object plane or an image of the object plane is located in a regionof a retina of the eye in the second mode of operation; wherein alateral width of the OCT measuring beam at the object plane in the firstmode of operation is greater than the lateral width of the OCT measuringbeam at the object plane or the image of the object plane, respectively,in the second mode of operation.
 2. The method of claim 1, wherein themicroscope system is configured to image the object plane onto the imageplane via an imaging beam path traversing an objective lens of theimaging system; wherein the OCT system further comprises OCT beamshaping optics which is located outside of the imaging beam path andwhich is configured to change a lateral width of a beam waist of the OCTmeasuring beam.
 3. The method of claim 2, wherein an OCT beam path ofthe OCT measuring light traverses the objective lens.
 4. The method ofclaim 2, wherein before and after the changing of the lateral width ofthe beam waist, the OCT beam shaping optics forms a substantiallyparallel beam bundle of the OCT measuring light.
 5. The method of claim2, wherein the OCT beam shaping optics has a variable focal length;wherein the changing of the lateral width of the beam waist compriseschanging a value of the variable focal length.
 6. The method of claim 2,wherein the OCT system is configured to direct the OCT measuring lighttoward the object plane via an OCT beam path; wherein the OCT beamshaping optics comprises a lens; and wherein the changing of the lateralwidth of the beam waist comprises inserting the lens into the OCT beampath or removing the lens from the OCT beam path.
 7. The method of claim2, wherein the OCT system comprises an OCT measuring beam emitter foremitting the OCT measuring beam; wherein before and after the changingof the lateral width of the beam waist, the beam emitter is located in afocal plane of the OCT beam shaping optics.
 8. The method of claim 2,wherein the changing of the lateral width of the beam waist compriseschanging a cross-sectional area of a substantially parallel beam bundleof the OCT measuring light.
 9. The method of claim 2, wherein the OCTbeam shaping optics is configured such that before and after thechanging of the lateral width of the beam waist, the OCT measuring beamis focused at the object plane.
 10. The method of claim 1, wherein anaxial field of view of the OCT system in the first mode of operation isgreater than the axial field of view of the OCT system in the secondmode of operation.
 11. The method of claim 1, wherein in the first modeof operation, the OCT measuring beam is focused at the object plane andin the second mode of operation, the OCT measuring beam is focused ontoat least one of the object plane and the image of the object plane. 12.An imaging system, which is configured to perform the method of claim 1.